Double Concave Mirror Image

mrjeffy321

I am trying to figure out how those double concave mirror set ups work to create an image above the mirror.
Does anyone know what I am talking about?

You have 2 [spherical] concave mirrors, both with the same radius of curvature (and thus the same focal length), one facing up, and the other facing down on top of the first. The mirror on top has a hole cut out of its center.
When you place an object in the center of the bottom mirror, an image of that object appears hovering in mid air over the hole cut in the top mirror.
If you need more clarification, see attached picture (the black square is the object, the gray square is the image).


Here is how I think it works, lets see if I am correct.
Since the mirrors have the same radius of curvature, then have the same focal length. Lets just say that the focal length just happens to be the distance between the ceneter of the top mirror and the center of the bottom mirror. So any object placed in the center of the bottom mirror emmits light that is relected (from the focal point of the top mirror) parallel of the top mirror. The the parallel light from the top is relected through the focal point of the bottom mirror (which is the center of the top mirror) and thus creates an image.
I further illustrated my idea on the attached image (the black lines emminating from the object bounce off the top mirror and are then shown by the green lines, which bounce off the bottom mirror, which then are shown by the blue lines becomming the image we see)

Attached Thumbnails

 

Doc Al

Your explanation is correct.

Here's an earlier thread on this device, but you have the idea: http://www.physicsforums.com/showthread.php?t=74837